It's actually a bit more like a hybrid of slack and ventrilo, but for fandoms and gaming. I primarily use discord for group chats and playing TTRPGs online. but I'm also in several podcast fan servers (official and unofficial) where a community of folks with common interests congregates.

Creators have really begun to actively use it to manage and engage with their fan-bases, and I bet there are some companies that use it as a slack alternative.

This isn't even mentioning the wide variety of bots and integrations for Discord, or how private text chats can enable/switch to audio or video communication.